Synthesis and characterization of nanocrystalline Ni0.94Co0.03Mn0.04Cu0.03Fe1.96−xAlxO4 ferrites for microwave device applications

•Ni0.94Co0.03Mn0.04Cu0.03Fe1.96−xAlxO4 has proven to be very useful for many microwave applications.•This is because of their relatively low magnetic and dielectric losses, high-Curie temperature, high saturation magnetization, low coercivity.•It is found that the presently investigated ferrites possess good temperature stability of saturation magnetization.•Because of excellent magnetic and dielectric properties present ferrites are suitable for the microwave devices with high power handling capability.

Nanocrystalline Ni0.94Co0.03Mn0.04Cu0.03Fe1.96−xAlxO4 (x=0, 0.1, 0.3, 0.5, 0.7 and 0.9) were synthesized using the microwave hydrothermal method at 160 °C/40 min. The synthesized powders were characterized using X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Fourier transform infrared spectra (FTIR). The nanopowders were densified using microwave sintering method at 950 °C/30 min. The prepared samples were characterized using XRD and Field emission scanning electron microscopy (FESEM). The substitution of nonmagnetic Al3+ ions in place of magnetic Fe3+ ions results decrease of the density and lattice constant. An increase in dc resistivity and reduction in the initial permeability, saturation magnetization (Ms) and Curie temperature (TC) has been observed with a substitution of Al3+ ions. High dc resistivity and low dielectric, magnetic losses combined with an excellent temperature stability of magnetization (4πMs) observed in the present ferrites can be explored for the fabrication of microwave device such as circulators, phase shifters etc.